This invention pertains to microlithography of a pattern, defined by a reticle, to a sensitive substrate using a charged particle beam such as an electron beam or ion beam. Microlithography is a key technology used in the manufacture of microelectronic devices such as integrated circuits and displays. More specifically, the invention pertains, in the context of charged-particle-beam (CPB) microlithography, to methods and devices for accurately determining proper times (e.g., prescribed intervals) for performing scheduled maintenance (e.g., cleaning or replacement) of certain components of the apparatus.
In recent years, as the critical dimensions of electronic devices in integrated circuits have become progressively smaller, the resolution limitations of optical microlithography have become increasingly apparent. Hence, much attention has been focused on the development of alternative microlithography technologies offering better resolution than optical microlithography. For example, microlithography using a charged particle beam (e.g., electron beam or ion beam) has been the subject of considerable development effort.
Although current charged-particle-beam (CPB) microlithography apparatus offer prospects of high resolution and exposure accuracy, the throughput obtainable with currently available equipment is disappointingly low. Various approaches are being investigated to improve throughput without adversely affecting image quality or imaging accuracy.
In one approach, the pattern to be transferred (by CPB microlithography) to a substrate is divided, or segmented, on the reticle into a large number of subfields or analogous exposure units that are exposed individually. This approach is termed xe2x80x9cdivided-reticlexe2x80x9d projection exposure.
Various components used in a CPB microlithography apparatus are subject to accumulation of contaminants, which can cause degradation or drift in performance of the apparatus. For example, irradiation of the resist layer on the substrate can cause outgassing of organic compounds from the resist. Also, CPB-optical systems (including reticle and substrate) must be evacuated during use. Components located adjacent to evacuation ports can become contaminated by deposits of oil from the vacuum pumps used to evacuate the CPB-optical system.
Hence, in any of various CPB microlithography approaches, in order to form accurate patterns consistently over time, cleaning of various components (e.g., electrodes, apertures, and the like) in the CPB-optical system must be performed. Conventionally, such cleaning is performed on a predetermined periodic basis, such as every six months or year. However, an optimal cleaning interval depends upon the conditions (e.g., beam current or frequency of rough pump-down) of use and how often or how much the CPB microlithography apparatus is used. Hence, attention currently is being given to establishing scheduled cleaning intervals based on experience, with appropriate margins applied.
However, whenever a problem such as significant beam instability arises (which can degrade pattern accuracy), cleaning of the CPB-optical system is indicated regardless of whether a scheduled cleaning is due. Contamination of the CPB-optical system usually is manifest as deposits of hydrocarbons (from outgassing of resist and residual vapor of pump oil) that adhere especially to components situated around the trajectory of the charged particle beam. The longer the apparatus is operated, the greater the volume of contaminant deposits. Deposits of contaminant hydrocarbons are usually electrically insulative. Deposits of insulative contaminants on an aperture or on the reticle entrap charged particles and thus experience localized xe2x80x9ccharge-up,xe2x80x9d which creates random electric fields in the vicinity of the deposits. The random electric fields perturb beam trajectory, with an attendant loss of transfer accuracy and resolution due to beam blur. The severity of charge-up varies with beam current and the actual amount of contaminant(s) in the respective deposits.
Whenever cleaning intervals are based on experience, certain systems may in fact go too long without being cleaned, or time may be wasted by cleaning certain components or systems more often than necessary. Failure to clean a system promptly when cleaning is necessary can degrade pattern-transfer resolution and increase distortions caused by beam deflections. These problems can be avoided by constantly monitoring and measuring of resolution and beam deflection. Unfortunately, such monitoring and measurements require large amounts of time and fail to identify individual components requiring cleaning.
In view of the shortcomings of conventional methods and apparatus as summarized above, an object of the present invention is to provide charged-particle-beam (CPB) microlithography methods and apparatus that provide accurate and timely information of the proper time (prescribed interval) for performing scheduled cleaning of the apparatus. Thus, the present invention solves problems such as degraded resolution and increased beam-deflection distortions caused by insufficient or inadequate cleaning. Another object is to provide semiconductor-device-manufacturing methods employing such microlithography methods and apparatus.
To such ends, and according to a first aspect of the invention, methods are provided (in the context of CPB microlithography methods) for detecting a time for a maintenance activity performed on a component in the column of a CPB microlithography apparatus. According to a representative embodiment of such a method, the component is subjected to a condition tending to cause release of molecules of a contaminant from the component to an atmosphere in the column. The atmosphere within the column is analyzed (e.g., by mass analysis) to detect an amount of a contaminant released from the component. From data produced during the analysis, a time for performing the maintenance activity of the component is determined according to the results of the detection. The condition to which the component is subjected can be, for example, irradiation of the component with the charged particle beam. The steps of irradiating the component and analyzing the atmosphere inside the column can be performed simultaneously and can be performed on multiple components in the column at the same time. The resulting data from the determinations can include times for performing the maintenance activity as determined individually for each component. The analysis can be performed at any of various times such as during startup of the column.
The method can include the step of determining a variance in beam positioning arising as a result of accumulation of the contaminant on the component. In this regard, the method can further include the step of determining a correlation between accumulation of the contaminant on the component and the variance in beam positioning. Data concerning the correlation can be stored in a memory for subsequent recall. Hence, the method can further include the step of recalling the data from the memory and determining the time for performing the maintenance activity of the component according to the recalled data.
Another aspect of the invention is directed to CPB microlithography apparatus that comprise a CPB-optical column. The apparatus includes a device for detecting an amount of a contaminant on a component of the CPB-optical column. According to a representative embodiment, such a device comprises a deflector situated and configured to direct a charged particle beam, propagating through the column, to impinge on the component and thus cause release of molecules of the contaminant. A sensor is situated and configured to detect the released molecules of the contaminant. The device also includes an analyzer (e.g., mass analyzer) connected to the sensor. The analyzer is configured to receive data from the sensor and to determine, from the data, a type and amount of the contaminant on the component. The apparatus can include a beam-position-measurement system situated and configured to detect a characteristic of a trajectory of the charged particle beam passing through the column. In such a configuration, the analyzer and beam-position-measurement system desirably are connected to a computer that is configured to determine a correlation between the detected amount of the contaminant and the characteristic of the trajectory of the charged particle beam.
The computer additionally can be configured to determine a time for performing a maintenance action on the component based on the determined correlation. The computer can include a memory situated and configured to store data from the analyzer concerning the contaminant, the state of use of the microlithography apparatus, and the history of prior maintenance activities concerning the component.
The sensor in the apparatus described above can be configured to detect molecules of the contaminant from the atmosphere inside the column.
The apparatus additionally can include multiple deflectors each situated and configured to direct the charged particle beam, propagating through the column, to impinge on each of multiple respective components in the column and thus cause release of molecules of respective contaminants from the respective components. Such an apparatus includes multiple sensors each situated and configured to detect the released molecules of the respective contaminant from the respective component. The apparatus also includes a respective analyzer connected to each sensor, wherein each analyzer is configured to receive data from the respective sensor and to determine, from the data, a type and amount of the respective contaminant on the respective component. In such an apparatus, the computer also can include a memory situated and configured to store data from the analyzer concerning the contaminant, the state of use of the microlithography apparatus, and the history of prior maintenance activities concerning the component. The computer further can be configured to recall data from the memory and to determine, from the recalled data, a time for performing a maintenance action on the component.
According to another aspect of the invention, semiconductor-fabrication processes are provided that include a method or are performed using an apparatus as summarized above.
In any event, by detecting the respective contaminant and contaminant level for one or more components in the CPB column, the timing of maintenance actions such as column cleaning or component replacement readily can be determined. By measuring, for example, contaminant molecules (e.g., hydrocarbon molecules) present in the atmosphere inside the column, column-maintenance procedures can be scheduled based on the measurements. Hence, the time at which cleaning or replacement will be necessary can be predicted with greater accuracy, thereby reducing degradation of pattern-transfer accuracy due to conditions such as charge-up and beam-trajectory variances. Furthermore, column maintenance can be performed at a stage in which maintenance can be performed readily without performing a major overhaul of the column. By performing contaminant detection simultaneously at multiple locations inside the column, the timing of component cleaning at various locations inside the column, as well as component replacement as required, can be determined individually for each subject location and component in the column according to the results of the detection. This provides detailed information as to which locations in the column have a contaminant buildup and which do not, thereby facilitating the avoidance of unnecessary maintenance work.
By determining a correlation between degree of contamination of a specific component and beam-position variance, detailed information can be obtained as to the degree to which the microlithography system is being degraded by contamination buildup (especially in terms of loss of resolution and beam-deflection distortion). This allows more informed decisions regarding the proper corrective action and when to take such action.